Prior to this change, a student would need to create their own tarball
if they wanted to only upload code to facilitate staff viewing their
code on the AG. This makes a source-only archive with no tests or
Makefile, to guarantee that a submission is not used.

Prior to this change, the remote path wasn't created safely and the
rsync command used would upload build artifacts to the remote.

Prior to this change, the comment directed users to "change EXECUTABLE"
which was the name of the variable whose value was supposed to be
changed. Users often changed the variable name instead of its value.

Prior to this change, remote path was built up with a subdirectory, but
without a separate call to ssh to create the sync root directory, rsync
would not create the leaf directory. In addition, all manner of goofy
filenames are used that include spaces, by people other than the author.
Some quoting and double-quoting has been added and cleaned up to
resolve (all of) these issues.

Prior to this change, the parent directory wasn't created and only
created leaf directories.

Prior to this change, we used test case and test file interchangeably,
but in an attempt to clear up wording, test case refers to the tests the
autograder applies, and test file refers to the tests the students
submit.

Prior to this change, the non-portable `echo -n` was used to list the
offending files without a project identifier during `make identifier`.
The proper way to do this is use printf.

This resolves issue #1.

% make all
This now builds executable, executable_debug, and executable_profile.
This will allow for easy implementation of the autograder building and
testing student solutions. When a SIG occurs, the AG can then run
valgrind with a debug build, to give improved feedback to students.

Build objects (.o files) are now only created for release builds.
Therefore, any .o file found in the directory will be compiled with -O3
and -DNDEBUG. The other two build targets (debug and profile) are
compiled directly from source to executable. This should prevent any
unfortunate hybrid builds.

Some minor documentation and formatting updates were also made.

Removed dos2unix; the autograder does fine without it (tested Project 1 Letterman), both source code and test files, and it produces headaches for students (especially those using Mfile)

Fixed 'identifier' to skip subdirectories, remove old tarballs if they exist, and tell user which files are missing the identifier

* A variable (IDENTIFIER) was added to allow the 'identifier' target to
  search source code and header files for a matching hash parametrically.
* The phony 'identifier' target greps for the IDENTIFIER pattern in each file
  and fails if any source/header doesn't contain the pattern.
* The identifier target is added as a dependency to fullsubmit and
  partialsubmit.
* Editing IDENTIFIER is now part of the first student TODO in the Makefile.

Added compiler version 7.1.0 before 6.2.0, just in case CAEN and autograder don't both have the same version available.  If both exist, should default to 7.1.0 (the first one in each path variable).

New target 'mac2caen' relies on SSH multiplexing, and an open SSH session
to keep files synced FROM Mac TO CAEN.

Slightly edited these targets (release, debug, all) for consistency.
Also picked some nits in comments and 'make help'.

* Previously we were checking all CPP files, we don't need to check
test drivers (test*cpp) for style.
* Instead of *.h*, use a more correct *.h *.hpp

Changed compile flag from -std=c++17 to -std=c++1z for Mac users; still works on CAEN and autograder.